Here are some recent preliminary test results on the grade pulling ability of some HO gauge Northern Pacific steam locomotives on a 16 foot long straight test track.
The Sunset 4-8-4 A-3 #2660 could not pull 10 passenger cars (due to slipping) on a 1.5% average grade, was marginal with 9 cars and was fine with 8 passenger cars (Walthers ‘light-weight’ cars). On a 2.7% average grade with 7 passenger cars it would slip and stall, but was fine with 6 cars. With 16 freight cars (proto, Athearn, and Roundhouse) it could start and go but was slipping, 15 freight cars was fine. BTW the prototype A-3 could take 10 heavyweight passenger cars up a 2.2% (compensated) grade, but needed a helper for more than 10.
A Sunset 4-6-6-4 Z-6 #5120 could not pull 6 passenger cars up the 2.7%, was marginal with 5 and fine with 4 passenger cars. IMO the decreased performance is due to the prototypically correct way the front set of drivers are attached to the rear frame so there appears to be little weight on the front set of drivers. For comparison a Model Railroader review earlier this year said that this engine could pull 54 freight cars on the level.
The Proto 2000 2-8-8-2 Z-4 #4502 (my renumber from 4503) could not pull 7 passenger cars up the 2.7% grade, but was fine with 6 passenger cars. I recognize that the low drivered Z-4 was not a passenger engine, but the test is a fair comparison. IMO the better peformance of the Z-4 vs the Z-6 probably stems from the fact that the front drivers of the HO Z-4 pivot on the front boiler and thus have more weight on them. Using the Z-4 as a helper in a consist with each of the other two produced the expected results (the sum of the individual results ie. 12 passenger cars with the A-3 and 10 cars with the Z-6).
Grinnell, why the pulling report? Not that it was not fun to read. If you are looking for a strong puller, see if you can find the PCM version of the Y6 b. (can’t say about the Blue Line version first hand) My PCM Y6 b pulled 60 coal cars up 1.5% grade at slower speeds with out a problem at K-10 Model Train Christmas Party few years ago.
I don’t think that the front engine operating in a prototypical way is necessarily the cause of the Z-6’s poor performance. The tractive effort is based on the weight on (powered) drivers and the coefficient of friction for the driver tires. Perhaps Sunset’s loco has poor weight distribution on the drivers, or maybe too little weight overall.
I’m curious how Sunset transferred the locomotive weight onto the front engine. How did they do that?
Ed
PS: I’ve got a Tenshodo GN 2-8-8-2 that is a notable puller, and it’s got a prototypically mounted front engine.
The Sunset A-3s and P2k Z-4s will be OK in freight service with a Z-4 helper on the climb to Mullan pass, but the Sunset Z-6 performance was certainly disappointing. We’ll have to see how the Z-6s actually perform on the 1% compensated grade (using 32/R grade compensation eg. a level 32 in radius curve would be theoretically equivalent to a 1% grade) from my future east-end staging westward up to Helengon (Helena, MT). Otherwise, I have a pair of nice “photo props”.
The boiler on the Z-6 model is cantilevered off the back end with no direct bearing surface to transfer weight to the front engine (and I doubt if the elbow joints in the steam pipes between the boiler and the front cylinders transfer any force in the downward direction). The locomotive itself seems reasonably heavy but I don’t see how there is much weight on the front set of drivers).
It looks like my version of the Northern Pacific is going to have to lease some “foreign” steam locomotives to maintain the schedule. I’m very interested in hearing the results of peoples’ experience with pull-tests of various HO steam locomotives. Because of the 32/R curvature effect, it would be most usefull if either the whole train was on reasonably straight track or on a stated continuous curve.
That is sad. We ended up with an unavoidable 5% grade coming out of staging at my local club. And yeah, things need a nudge from the back to get going, but every engien I’ve taken there has gotten at least itself and part ot the train to the peak beofre snortin’ and snarlin the rest. That’s included a Heritage 0-8-0 saddle even with a MRC, that willingly charged up (and took) that hill with a cut of 12 40ftrs (accurail and Bowser mostly) no problem. It must just be the weight on his drivers, but sad that little guy out pulled a Brass 484
It shouldn’t be too surprising that a switcher might outpull a 4-8-4. The NP A-2 was rated at 69,800 lbs tractive effort. PRR and NYC, for two examples, had 0-8-0s that easily exceeded that. The PRR C 1 was good for 78,107 lbs and the NYC U-4a made 75,700 lbs. The U-4 also had a booster on its tender that added another 13,000 lbs. A little research might turn up more of the same.
In HO scale, the variable that makes the most difference is the rolling quality of the freight trucks. I doubled the length of my trains by replacing all freight car wheels with Branchline semi-scale wheels. You may prefer another brand, but the result will be stunning. A freight car with a standard-issue wheelset will most likely not roll down a 1% grade, but it will accelerate down the same grade with free rolling wheels. The downside of free rolling wheels is that sometimes you want the train to sit still and it won’t.
Well, my locos aren’t models of NP locos, but they seem to pull respectably. After reading this thread, I was prompted to run a test train up one of my 2.5% hills. The grade in question travels just over 3’ on straight track, then curves to the right on a 33" radius. This is followed by just under 3’ more of straight track, followed by a left-hand curve, also on a 33" radius, then a final 3’ of straight track. The grade is constant except for vertical easements at the top and bottom, and the total length of the grade is just over 17’.
For a test train, I used Accurail wood sheathed cars - reefers and boxcars, all at a stock weight of 4oz. each and all rolling on their original plastic wheels. Bringing up the rear was a modified Athearn caboose weighing 5.75oz, and running on Tahoe Model Works trucks. Motive power was a Bachmann 2-8-0, slightly modified with additional weight. Loco weight was 15oz., plus another 6.25oz. for the tender.
With limited wheelslip (within acceptable limits) on the final straight, the loco was able to take 18 cars, plus the caboose, up the grade. I would expect a similar performance from my modified Athearn Mikes.
Thank you Dr Wayne, that was just the kind of very usefull information I was looking for. (BTW, I’ve enjoyed the pictures of your layout and rolling stock, great work.)
To a first approximation, the grade you describe is roughly equivalent to 3% on a straight hill. A 33" radius curve adds just short of 1% to the actual 2.5% and with a little less than half the distance curved it all averages out to about 3%. Nineteen cars (including the caboose) with a consolidation up 3% is really good, maybe better than in the real world. There was a railroad back east that used to tack 7 to 10 consolidations on coal drags, but I’ve forgotten the exact details. I do remember reading and being impressed that Union Pacific used 3 challengers (front, mid and rear) to haul 75 car freights over the 3% grade up Monida pass on the line from Idaho north to Butte, MT.
I’d been thinking about the Bachmann 2-8-0 for my eventual Montana Central (ex GN) line from Great Falls, MT through Helengon (Helena) up to Infinity (Boulder) and beyond to Jones Butte (Butte, MT). Looks like my NP could use a mythical Class F-9 consolidation (that’s what decals are made for) so I don’t have to try to turn a Bachman 2-8-0 into an NP class F through F-8.
If you can work one of those locos into your roster, I’m sure you’ll be pleased with its performance. I added about 2.25oz. of balanced weight to mine, but they’re decent pullers right out of the box. I use a pair of them to haul a 100oz. coal train (12 hoppers and a caboose) up the same grade (and another similar but much longer grade). In mixed freight service, a single loco usually handles 10 to 15 cars.
If you can add a couple of NP-specific details (that distinctive headlight comes to mind) plus proper NP paint and lettering, it should make a respectable stand-in.
I’m running DC and often doublehead mine with my Athearn Mikes, and, when I still had them, with various diesels - they’re real workhorses.
Incidentally, the loco which I used for the test was the one the crews call the “Lucky 26”.
She suffered a scale 250’ drop, pilot first, to the concrete floor. The only damage incurred was a snapped-off drawbar pin on the tender and the wires pulled from one of the plugs. The drawbar pin was an easy repair, but threading the wires back into the plug took a little more time. Since I’m running DC, I eventually removed the circuit boards from all of these locos and simplified the wiring set-up, with only two wires between loco and tender.
Here are some additional test results with freight cars on the 2.7% straight grade.
As Flashwave suggested earlier in this tread, the P2k 0-8-0 G-1 #1171 turned out to be “the little engine that could”. With 25 freight cars it started nicely with minimal slip and accelerated briskly so I quickly ran out of test track. With low drivers and all it’s weight on the drivers it is a pulling little machine. Too bad it will spend its life on the flat in the yard. IRL the NP G-1 weighed 214,000 lbs and had a tractive effort of 51,200 lbs while the Z-4 weighed 514,500 lbs and had 117,300 lbs tractive effort. The HO version of the Z-4 was OK with 17 freight cars but seemed to be on the ragged edge of stalling with 18 cars. The real Z-6 weighed 624,500 lbs and had a 104,500 lb tractive effort. The HO version of the Z-6 was fine with 11 cars but marginal (on the verge of stalling) with 12. The real A-3 weighed 491,800 lbs with 69,800 lbs of tractive effort. As reported earlier the HO version of the A-3 was fine with 15 cars and marginal with 16.
In an attempt to make this a little more ‘scientific’ I tried my brand new Micro-Mark Digital Pull meter. With 11 freight cars on a 2.7% grade it measured 0.8 oz to hold the cars from rolling down the grade and 1.0 oz to move them steadily up the hill. I think this implies that if I had the perfect frictionless axle bearings we would’t see this 0.2 oz and thus see a 25% improvement in performance. I don’t have a decent scale (obviously need to get one) so I’ll have to just assume that the cars weigh 4 oz each, times 11 cars, times .027 gives 1.1 oz trying to accelerate the cars down the slope, minus 0.2 oz of friction yields 0.9 oz that my pull meter has to exert to keep the cars from rolling down the hill which is close to the 0.8 oz that were measured.
There is a big ‘however’ in this: Micro-Mark says “The meter is capable of reading in increments of .005 kg. This is equivalent to 0.17 oz.” So in this case the lack-of-precision of the meter is about equa
If you want a Z6 that will actually “pull” like it has real power I would suggest one of the older Tenshodos. You can find them for about half what a Sunset version will cost and they’re built at least twice stout. I have a couple that I inherited from my Dad that he bought in 1972 and installed Sagami motors in, they are still running as beautifully as they did in 1972 and will easily pull 50 free rolling freight cars up and over a 2% grade without a whimper and although I have not compared them side by side I would guess that the detail level is at least as good as the Sunset.
On the four Bachmann Consolidations currently in service, I added weight in the form of (custom cast) lead blocks atop the frame and between the drivers - these are insulated from the frame with electrical tape, but otherwise just sit in place. I also added an air tank on the pilot deck - it’s a piece of brass tubing into which I poured molten lead. Careful placement ensured that the total weight remained balanced about the mid-point of the drivers’ wheelbase.
I use a “standard train” as a test for all locomotives operating on the layout - it consists of an Athearn caboose weighing 4 oz. and 12 Athearn two-bay hoppers, all with “live” loads and each weighing 8 oz. This is the heaviest regularly-scheduled train that operates, and requires two locomotives (Athearn Mikes or Bachmann Consolidations, in any combination) to move it over all of the grades encountered.
All locomotives are tested with such a train, with hoppers removed one-at-a-time until the loco can make it up the grade unassisted and with minimal wheelslip.
I assign each hopper (and the caboose) a nominal weight of 70 tons, and base each loco’s “tonnage rating” on the number of hoppers which it can move up that hill. Since most regular freight cars aren’t this heavy, I have some leeway and generally rate mixed freight at 50 tons per car. A loco that can move 4 hoppers and a caboose is rated at 350 tons, and is good for seven “regular” freight cars. If one of those cars happens to be a loaded hopper, I’m confident that the loco has enough “in reserve” to get the job done. However, for two or more loaded hoppers, the car count goes down accordingly.
If I have a train of, say, 550 tons, I might use any two locos that have a total rating of at least 550 - it could be more, but never less unless I’m prepared to “double the hills”. This assumes, of course, that all of the locos used run well with one another - only one currently in service doesn’t always meet this
That pretty much reflects my experience with my Tenshodo articulateds. On my Z-6, I notice a leaf spring bearing down on the top of the front engine. I’ve also got an old Sunset UP 2-8-8-0 (wow, they were little engines). That little fella has an even more ingenious arrangement–there’s a sprung plunger pushing down on a piece of sheet metal arranged side to side on the top of the front engine. It’s sort of a slight V shape. I think what that’s supposed to do is to help center the engine. Pretty clever!
If your Sunset Z-6 has no weight transfer to the front engine, it sure isn’t going to pull much (assuming, of course, that the front engine is powered). If you’re going to keep the engine, you might want to add some weight in the boiler and make sure the weight is distributed nicely to the two engines. If there’s not weight-transfer “spring” for the front engine, you’ll have to add one.
I did the tonnage test with the 0-8-0, then discovered test records that showed a previous test of the modified loco. [D)] The results, not surprisingly, were the same: four loaded hoppers and the caboose and a 350 ton rating. The records also show that the original loco and tender weighed in at 14.5oz., while the modified version is 18oz., of which 12.5oz. is represented by the loco alone.
Here are more pull test results with freight cars, this time on a 1.55% average grade and straight track. [The test rig is 2 pieces of 10" x 8’ 3/4 inch birch plywood screwed to 1x3 girders on edge with a 6" overlap at the joint and 1x3 doublers at the joint. The rig is supported off the floor in 4 places with various thickness shims. If I did it again, I’d use 1x4 L girders to make it stiffer. I measured the grade at 1’ intervals with a Micro-mark digital level (a really neat tool that is almost too precise for benchwork construction - who knew that 3/4 plywood could be so waverly?). The top 5 feet averaged 1.72%, the next 5 averaged 1.51% and the bottom 5 averaged 1.42% for an overall 1.55%.]
The good news here is that the Sunset Z-6 4-6-6-4 performed much better at the 1.5% grade: it could start, but had lots of slip and stalled with 21 freight cars; with 20 it seemed to be on the verge of stalling; 19 slipped but was OK and 18 was fine with minimal slip. My planned west-end staging tracks should hold the engine and up to 23 cars and have a 1.3% compensated uphill grade, so it looks like the Z-6 will work in freight service. If it turns out to be marginal, I’ll experiment with better wheels on the reefers and stock cars and initially assign the Z-6s to the fruit manifest and the stock extra. It also looks like there is room below the boiler to put some weight on top of the front engine sub-frame (yes it is powered).
The Sunset A-3 4-8-4 could start, accelerate with some slipping but seemed to be a little iffy at the steeper top end with 24 freight cars. It was fine with 23 cars which is what I need.
The P2k Z-4 2-8-8-2 easily pulled 25 freight cars, I couldn’t test more because I ran out of room on the test rig.
Dr Wayne, thanks for the good explanation of where and how to add more weight. Having a ‘standard test train’ and operating with tonnage ratings for your locomotives is a really neat idea. The is only one word to describe my reaction to your last two pictures: "awestr
I don’t have the Sunset Z-6, but I do have several Sunset brass locos, and one thing I’ve found with them is that though they are smooth runners, they are not balanced very well as far as weight. They seem to be a little ‘cab-heavy’ as far as distribution, and the one articulated that I have (an SP AC-6 4-8-8-2) had to be re-weighted and re-balanced with additional weight toward the front of the boiler to get the maximum traction effort out of it.
I don’t know if the Z-6 has a spring mechanism between the front of the boiler down to the lead driver set, but I would think it should. Most of the brass articulateds I own (and it’s quite a few, BTW) have some sort of spring-loaded protrusion from the bottom of the boiler down to the front set of drivers, to give them additional trackage. If the Z-6 doesn’t (which would surprise me), you might want to think of fabricating one.
I don’t know how difficult the newer Sunset Models are to disassemble to take the boiler and cab off of the mechanism (the older ones could be removed with about four or five screws), but you might want to think of some additional weight toward the front of the boiler,a little ahead of the rear driver cylinders. This might give the locomotive a little more even ‘balance’ overall. I did that with my AC-6, and it improved the tractive effort by almost 50%. It will haul as much now as my much older Max Gray AC-12, and believe me, that’s a LOT!
